Let's do some math ..  Rounding examples of 7 random hypothetical purchases:
Case	Tag   Price	Sales   Tax %	Raw Total   Incl. Sales Tax	Rounded   to Penny	Rounded   to Nickel	Rounded   to Dime
Purchase #1	$209.78	5.777%	$221.899	$221.90	$221.90	$221.90
Purchase #2	$140.35	7.104%	$150.3205	$150.32	$150.30	$150.30
Purchase #3	$29.90	5.297%	$31.4838	$31.48	$31.50	$31.50
Purchase #4	$206.39	13.827%	$234.9275	$234.93	$234.95	$234.90
Purchase #5	$212.45	4.599%	$222.2206	$222.22	$222.20	$222.20
Purchase #6	$22.37	12.211%	$25.1016	$25.10	$25.10	$25.10
Purchase #7	$189.40	11.703%	$211.5655	$211.57	$211.55	$211.60
7 purchase totals =	$1,010.64		$1,097.5185	$1,097.52	$1,097.50	$1,097.50